This invention relates to a signal transmitting system for a rotary magnetic head utilized for an information recording and reproducing apparatus, and more particularly, to a current transmitting mechanism therefor for transmitting an electric signal between a rotating element and a non-rotating element.
There is known a rotary head device utilized for an information recording and reproducing system such as a video tape recorder (VTR) or a digital audio tape recorder (DAT), in which a rotor of an electric motor and a rotary drum of the motor to which a magnetic head is attached are mounted on a rotating shaft of the motor to integrally rotate the rotor and the rotary drum together with the rotating shaft of the motor. Such a magnetic head device is provided with a magnetic head secured to the rotary drum so as to be rotatable and a current transmitting mechanism for transmitting a signal to a non-rotatable body of the magnetic head device.
In the initial stage of the development of the VTR, such a current transmitting mechanism is provided with a slip ring attached to the rotary drum and a brush element attached to a non-rotatable stationary drum, and an electric signal is transmitted by virtue of the slidable contact between the brush element and the slip ring.
The current transmitting mechanism of the structure described above can be produced with relatively low cost, but is disadvantageous because of the generation of noise due to the sliding contact between the brush element and the slip ring, and because of reduced life time in use due to frictional wear therebetween.
The noises due to the sliding contact generally increase in accordance with the change of the mechanically contacting condition between the brush element and the slip ring. For example, the brush element is subjected to a contacting force at the contacting front portion thereof, thus generating vibration which is one factor of the degrading performance of the mechanical contact. In order to obviate this defect, there has been proposed a current transmitting mechanism capable of maintaining a stable contacting condition by utilizing a plurality of brush elements, each for one signal transmission means, having shifted resonance frequencies, respectively (for example, refer to the Japanese Utility Model Publication No. 48-36665 (36665/73). However, in such a current transmitting mechanism, a plurality of brush elements are required for one channel, which requires additional space for the location thereof. For example, there is known a small size micro-motor provided with a pair of noble metal brush elements between which a slip ring is disposed. The brush elements and the slip ring are contacted during the rotation of a rotor of the micro-motor. The noble brush elements vibrate with characteristic frequencies during the contact to the slip ring so as to thereby contact to or separate from the slip ring. For the reason described above, and as illustrated in FIG. 5 and FIG. 6, the noble metal brush elements 31 in a micro-motor 32 are composed of a plurality of, three for example, parts 31a, 31b and 31c having different lengths and different characteristic frequencies from each other so that at least one of the three parts always contacts the slip ring. In the micro-motor as the current transmitting mechanism of the type described above, since a plurality of brush elements are needed, additional space for the location thereof is required.
In view of the above, about a motor, a brush contacting mechanism has not been employed actually and, a brushless motor has been employed. While, in a signal transmitting mechanism between a rotary magnetic head and a non-rotary element, recently, a non-contact rotary magnetic head device provided with a rotary transformer has been utilized as a current transmitting mechanism.
Since the rotary transformer is an ordinal transformer and thus has a common function such that the transfer loss is reduced as the coupling coefficient between the windings of a rotor and a stator becomes large, it is desired for the the rotary transformer to have a small gap between the rotor and the stator and to have large opposing areas of the cores of the rotor and the stator. In such a non-contact type current transmitting mechanism, the mutual contact between the respective magnetic cores is prohibited, which results in the requirement of improved working and assembling tolerances and performances. Thus, the manufacturing labor and cost may be increased. The increasing of the contact areas of the cores may result in the enlargement of the transformer itself, i.e. a drum assembly to which the transformer is mounted. Accordingly, the non-contact type current transmitting mechanism also has the disadvantages described above.